The well known low voltage bandgap buffer apparatus is an indispensable part in a bandgap system. In practice, this apparatus can compensate for the voltage variation of a bandgap circuit which has the advantage of promoting a circuit system architecture design that uses a transistor with a low operational voltage. However, it is more and more difficult to design this buffer in a low voltage environment, especially when there is no low threshold (low Vt) device available.
In the other aspect, the purpose of providing a stabilized voltage source to a circuit without subjecting it to temperature fluctuations, other voltages, and environmental changes is conformed with the requirements of electrical characteristics of transistor hardware from the circuit design software point of view, such as field-programmable gate arrays (FPGA) and application-specific integrated circuits (ASIC). Therefore based on the trend of transistor sizes becoming miniaturized, this voltage buffer apparatus having the capabilities of stabilizing the voltage source and providing applications for high-level circuits needs to be further improved to promote its key role in the circuit system design.
Please refer to FIG. 1, in a conventional voltage buffer apparatus which contains a voltage source 105 and a ground 106, an input signal 101 is magnified with the first degree from an operational amplifier 10 and then with the second degree from a transistor 11 which is connected to the output terminal 103 of the operational amplifier 10 for providing a stabilized output voltage 104 to the next circuit stage, wherein the variation factor of the input signal 101 can be compensated with the modulation of a feedback voltage 102 which is subject to a first variable resistor 12. Yet the feedback voltage 102 can not be transmitted by using MOSFET in the condition of low voltage, it is to say that the feedback route is not capable to proceed useful compensation within this architecture.
In the other hand, the changing method of the first variable resistor 12 is having different values of resistors in the upper section and lower section with respect to the feedback node such that the feedback voltage 102 is high when an adjusting switch 13 being located on the first position 131 and is low when the adjusting switch 13 being located on the second position 132. However it is not satisfied with the demand of a simplified device value changing when performing voltage adjustment in the circuit architecture with above mentioned method for the requirement of analysis and control of the circuit operation. Therefore it is necessary to do some improvements in the architecture of the voltage buffer apparatus for fulfilling the goals of electrical characteristic match and reliable operation of the device in the prevalent usage of the voltage buffer apparatus for bandgap system.
From above mentioned, a new voltage buffer apparatus for bandgap system is needed urgently. Thus, based on the drawbacks of prior art, the inventor gave the utmost attention and finally invented the voltage buffer apparatus for bandgap system with experiment and research. Based on the spirit to work with perseverance, the problem of prior art was solved. The particular design in the present invention not only solves the problems described above, but also is easy to be implemented. Thus, the invention has the utility for the industry.